In mammals, e.g., humans, when the kidneys and/or liver fail to remove metabolic waste products from the body, most of the other organs of the body also soon fail. Accordingly, extensive efforts have been made to discover safe and effective methods for removing toxins from patients' blood by extracorporeal treatment of the blood. Many methods have been proposed for removing small molecular toxins, protein-bound molecules or larger molecules thought to be responsible for the coma and illness of hepatic failure. Some of these toxic compounds have been identified as urea, creatine, ammonia, phenols, mercaptans, short chain fatty acids, aromatic amino-acids, false neural transmitters (octopamine), neural inhibitors (glutamate) and bile salts. Among these, phenols and mercaptans, along with bilirubin and bacterial endotoxins, also occur as strong protein-bound toxins and are thus more difficult to effectively remove from the blood. Middle molecular weight toxins having a molecular weight of about 300 to about 10,000 can also be present and are difficult to effectively remove.
The art shows a number of ways to treat blood containing such toxins. The classic method is of course dialysis. Dialysis is defined as the removal of substances from a liquid by diffusion across a semipermeable membrane into a second liquid. Dialysis of blood outside of the body (hemodialysis) is the basis of the "artificial kidney." The artificial kidney treatment procedure generally used today is similar to that developed by Kolff in the early 1940's.
The art contains a number of disclosures which deal with improvements on artificial kidneys or artificial livers. Thus, U.S. Pat. No. 4,261,828 discloses an apparatus for the detoxification of blood. The apparatus comprises a housing filled with an adsorbent such as charcoal or a resin and optionally an enzyme carrier. In order to prevent direct contact between the blood and the adsorbent, the adsorbent may be coated with a coating which is permeable for the substances to be adsorbed yet prevent the direct contact between the corpuscular blood components and the adsorbents. U.S. Pat. No. 4,581,141 discloses a composition for use in dialysis which contains a surface adsorptive substance, water, a suspending agent, urease, a calcium-loaded cation exchanger, an aliphatic carboxylic acid resin and a metabolizable organic acid buffer. The calcium loaded cation exchanger can be a calcium exchanged zeolite. Finally, U.S. Pat. No. 5,536,412 discloses hemofiltration and plasmafiltration devices in which blood flows through the interior of a hollow fiber membrane and during the flow of blood, a sorbent suspension is circulated against the exterior surfaces of the hollow fiber membrane. Another step involves having the plasma fraction of the blood alternately exit and re-enter the interior of the membrane thereby effectuating removal of toxins. The sorbent can be activated charcoal along with an ion-exchanger such as a zeolite or a cation-exchange resin.
There are problems associated with the adsorbents disclosed in the above patents. For example, charcoal does not remove any water, phosphate, sodium or other ions. Zeolites have the disadvantage that they can partially dissolve in the dialysis solution, allowing aluminum and/or silicon to enter the blood. Additionally, zeolites can adsorb sodium, calcium and potassium ions from the blood thereby requiring that these ions be added back into the blood.
Applicants have developed a process which uses microporous ion exchangers which are essentially insoluble in blood or dialysis solutions. These microporous ion exchangers have an empirical formula on an anhydrous basis of: EQU A.sub.p M.sub.x Zr.sub.1-x Si.sub.n Ge.sub.y O.sub.m (I)
or EQU A.sub.p M.sub.x Ti.sub.1-x Si.sub.n Ge.sub.y O.sub.m (II)
where A is an exchangeable cation selected from the group consisting of potassium ion, sodium ion, rubidium ion, cesium ion, calcium ion, magnesium ion, hydronium ion or mixtures thereof, M is at least one framework metal selected from the group consisting of hafnium (4+), tin (4+), niobium (5+), titanium (4+), cerium (4+), germanium (4+), praseodymium (4+), and terbium (4+), except that M is not titanium in formula (II), "p" has a value from about 1 to about 20, "x" has a value from zero to less than 1, "n" has a value from about 0 to about 12, "y" has a value from 0 to about 12, "m" has a value from about 3 to about 36 and 1.ltoreq.n+y.ltoreq.12. The germanium can substitute for the silicon, zirconium/titanium or combinations thereof.